You probably have heard the cautionary words, Correlation is not causation. So, we should ask: Even if there are correlations in the data between neutering status and certain disease outcomes, do those correlations represent a cause-and-effect relationship? One common relationship that is not cause-and-effect is known as reverse causation. Consider, for example, a group of purebred puppies whose owners were advised to have their dogs neutered at a young age because a littermate had an unusual gait or improper conformation that has a genetic cause. An analysis of the data on these dogs later in life—that does not account for the reasons for neutering and the order of events—could very well make it look like the early neutered dogs were at higher risk of joint problems. But the interpretation is erroneous: The propensity for joint problems prompted the pediatric neutering; the neutering did not cause joint problems.

The studies we discussed in the first part of this series did not collect data on reason for neuter, and made little attempt to assess which relationships could be explained by a reason that is not cause-and-effect. As a result, readers are left with the false impression that all the outcomes were caused by the choice to neuter (or choice to neuter at a particular age). They are also left with the implication—likely incorrect, in some cases—that the health outcomes could be averted by delaying or avoiding neutering. Unfortunately, in these studies, it is nearly impossible to tease out which of the relationships are cause-and-effect and which aren’t.

"If in doubt, never hesitate to consult with your friendly neighborhood epidemiologist!"

Intentionally misleading headlines?
To compound the limitations of these studies, reports on them cherry-picked findings that supported an anti-neuter perspective. A friend of mine, for example, shared articles on Facebook featuring Dr. Hart’s study with headlines that stressed the negative outcomes in the studies:

Early neutering triples risk of joint disorders in German Shepherd Dogs

These reports either did not mention the conditions that were reduced with neutering, or they only mentioned those findings near the end of the story, long after many social media readers would have stopped reading. And the reports certainly didn’t cover any of the studies’ limitations. While technically accurate, these reports appeared to be intentionally misleading and, as a result, verging on fake news.

Transparency about funding sources is also critical for earning readers’ trust and helping them make an informed decision about possible influence of the funding sources on data interpretation and reporting. None of the reports I read mentioned the complete name of the funding source (the American Kennel Club Canine Health Foundation), an organization which might be expected to have an opinion on the topic of neutering purebred dogs, and the reluctance to mention the full name of the funding source is concerning.

In these 2 blogs, I have covered a few (but not all) of the limitations of the recent studies on health effects of neutering and their reporting. So, what can you do if you see a new study claiming to find health risks or benefits of neutering in dogs? Or if clients or veterinarians are using studies to oppose your practices?

3 questions to ask about research reports
Consider asking yourself—and the folks you’re discussing the topic with—a few questions, such as:

Did the researchers study a general population of dogs (rather than those seen at a specialty center)?

Is the reporting fair and balanced? Does it cover both risks and benefits? Does it cover the study limitations?

Is the reporting transparent about who funded the study?

If the answer to any of these questions is “No,” then I would be concerned about biases in the study or its coverage. And of course, if in doubt, never hesitate to consult with your friendly neighborhood epidemiologist!

How does your organization approach spay/neuter of shelter pets—and services provided to your local community?

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Vic Spain, DVM, PhD

ASPCA Senior Director, Applied Research

Dr. Vic Spain’s current research includes effectiveness of animal-related legislation, assessing state and local emergency preparedness for animals and methods for connecting consumers to higher welfare animal-based food products. Dr. Spain received his Doctorate of Veterinary Medicine from the University of California, Davis and later attended Cornell University, where he received a PhD in Epidemiology with a graduate minor in biostatistics.